1. Field of the Invention
The present invention relates to a phase-change memory, and more particularly, to a phase-change memory that uses a semimetallic thin film formed of a phase-change material of a single-element, thereby increasing a write speed of the phase-change memory compared with the case of conventional Ge—Sb—Te (GST) material.
2. Description of the Related Art
A phase-change memory represents a device using difference in electrical resistance between a phase-change material in an amorphous phase and a phase-change material in a crystalline phase as a signal. Phase transformation between an amorphous phase and a crystalline phase is performed by Joule heating generated by an electrical current. Generally, in a phase-change memory, phase transformation from an amorphous phase to a crystalline phase is referred to as an operation SET, and phase transformation from a crystalline phase to an amorphous phase is referred to as an operation RESET.
In general, a Ge—Sb—Te (GST) based material is used as a phase-change material in a phase-change memory. When a semiconductor thin film formed of such a binary or ternary compound repeatedly crystallize and amorphize, the semiconductor thin film may seriously deteriorate, mainly due to the phase segregation. As a result, endurance of phase-change memory becomes significantly impeded. For example, in the case of GST, the atomic ratio of Ge, Sb and Te needs to be always maintained as 2:2:5 (i.e., Ge2Sb2Te5), so as to ensure that phase segregation does not occur. However, in a real situation in which GST is repeatedly crystallized and amorphized, it is well known that a significant amount of Sb is segregated and the atomic ratio of GST is not maintained as 2:2:5 any longer. Also, it is very difficult to correctly adjust the atomic ratio of 2:2:5 in semiconductor fabrication and for developing sources for chemical vapor deposition (CVD), atomic layer deposition (ALD) or the like, which is essential for integrating a phase-change memory.
In addition, when a compound with many elements is used to form a phase-change layer, it takes a long time for each elemental atom constituting the compound to be placed on respective atomic sites during an operation SET for crystallization, thereby slowing down the operation SET.